To slip a punch means to get your head out of the way. There are several ways to slip a punch and each way has merit. In some cases, one technique works better than others for a particular situation. I will be showing 3 variations of the slip. The key with any form of slipping is not to exaggerate the movement. You do not want to dip or bend so far that you hurt your back, lose your balance or take yourself out of position to counter.1. The first and most basic form of slipping a punch is what I call the side slip. When fighting at long range (where jabs & crosses barely connect), tilt your upper body (torso) slightly to the side. Maintain a defensive position throughout; keep your hands up around your face. Being at the distance makes it difficult to retaliate which is why this form of slipping is best. This doesn't improve your chance of landing your own punch, but it gets your head out of the way.
2. The second form of slipping is the inward slip. This is used at mid-range (where all punches can land). To execute the inward slip, simultaneously bend at the knees and waist slightly (don't hurt your back) at a 30 to 45 degree angle from the jab or cross, preferably to the outside of the punch. This is a very risky move, because if your timing is off, you will collide with your opponent's punch (see Zab Judah versus Kostya Tszyu). However, if done correctly, it will put you in a safe position to counter and makes it difficult for your opponent to land his follow-up punch effectively.
3. The third variation I would like to cover is what I call the rolling slip. Once again, this is best used from mid-range. This is a combination of a shoulder-roll and inward slip. As your opponent's jab or cross comes at you, turn your upper-body away and down. Don't forget: do not just use your back, bend at the knees as well. This technique is good if you do not want to use much footwork or prefer to save energy. Like the side and inward slips, try to go to the outside of the punch. If you are slipping the jab, you can counter immediately with the cross-hook. If you are slipping the cross, you can retaliate with the cross-hook. All this without having to take a step in or to the side.